Question

Recently I ran into a problem: Valid JSON when passed to the eval() function causes it to throw the error — “script stack space quota is exhausted”.

It is consistently reproducible, and through initial examination, it seems that this is a limitation on the number of object attributes/properties that can be defined (and not the size of the content).

Here’s the sample code:

function starttest()
{      
       var d = new Array(50000);
       var i = 0;

       for (i = 0; i < d.length; i++) {
            d[i] = new Object();
            d[i].a1 = 1;
            d[i].a2 = 2;
            d[i].a3 = i;
            d[i].a4 = i;
            d[i].a5 = i;
            d[i].a6 = i;
            d[i].a7 = i;
            d[i].a8 = i;
            d[i].a9 = i;
            d[i].a10 = i;
            d[i].a11 = i;
            d[i].a12 = i;
            d[i].a13 = i;
            d[i].a14 = i;
            d[i].a15 = i;
       }       



    var jsonString = JSON.stringify(d);  
    alert(jsonString.length);

    var obj = eval(jsonString);
    var count = 0;
    for( var i = 0; i< obj.length; i++) {

        for (var k in obj[i]) {
            if (obj[i].hasOwnProperty(k)) {
               ++count;
            }
        }
    }

    alert("Done! || Len: " + obj.length + " || " + "Attrib Count: " + count + " || " + typeof obj)
}

The funny thing is I can define many more objects than seen in the code snippet; the problem arises only when using the eval() function.

Any new insights into this would be greatly helpful. I know using eval() is not safe, and all… and I’m open to suggestions!

Answer 1

Yeah, this is a problem with Firefox’s JavaScript interpreter in general. It’s not just eval: if you put fifty thousand lines of:

{a:1,b:2,c:3,d:4,e:5,f:6,g:7,h:8,i:9,j:10,a2:1,b2:2,c2:3,d2:4,e2:5,f2:6,g2:7,h2:8,i2:9,j2:10},

in an array literal in a plain script file or <script> element, you get exactly the same error.

It seems the complexity of a script block is limited by the compile-time JS_DEFAULT_SCRIPT_STACK_QUOTA. See 420869 and the related linked bugs.

It’s relatively unlikely you should meet this in normal circumstances. Of course for the case of JSON you can use JSON.parse which, not being a full JavaScript interpreter, is not affected by this limitation. If you needed a non-valid-JSON JS literal parser that’s not affected, I guess you’d have to write it yourself… though it’d probably be annoyingly slow when you get to input this long.